Enhanced proton conductivity of hybrid membranes by incorporating phosphorylated hollow mesoporous silica submicrospheres

Hollow mesoporous silica submicrospheres (HMSS) are prepared with one-dimensional hexahedral mesopores regularly aligned along the radial directions of the silica shells. Both the outer and the inner surfaces of the mesoporous shells, as well as the mesopore walls are phosphorylated (PHMSS). Moreover, the lumen of PHMSS serves as accommodation for amino tris(methylene phosphonic acid) (ATMP) with large amount of phosphoric acid groups. Phosphorylated submicrospheres (PHMSS-ATMP) with multi-functionalities are thus prepared. After incorporating PHMSS-ATMP into chitosan (CS) matrix, the hybrid membranes were fabricated. The water uptake, anti-swelling properties and the proton conductivities are all enhanced. Particularly, the proton conductivities are considerably elevated and the highest proton conductivity is 9.4×10 −2   S   cm −1 at 110   °C 100% RH for the membrane with 7.5   wt% of PHMSS-ATMP; the proton conductivities of CS/PHMSS-ATMP hybrid membranes at 80   °C and low humidity are increased by two orders of magnitude compared to the pristine CS membrane. The enhanced performance could be attributed to the proton conducting groups introduced by PHMSS-ATMP: –PO 3 H 2 groups are anchored on the surface of PHMSS-ATMP, and proton conducting channels could be formed by the mesopores of the silica shell, and the lumen could serve as acidic reservoirs.